1. Field of the Invention
The present invention relates to a super-antigen fusion protein and the use thereof and, more particularly, to a fusion protein which binds to an antigen-presenting cell for inducing antibodies effectively, so as to suppress the virus infection and block the super-antigen response.
2. Description of Related Art
A virus is too small to propagate independently, and has to survive in a host cells by way of parasitism. Hence, viruses are classified in a species between organism and non-organism. Coronavirus is a single-strand RNA virus, and the way it enters cells is by binding to a target cell receptor and forming a cyst, then the virus enters host cells through endocytosis. The viral ribonucleic acid (RNA) reverses to DNA via reverse transcription, and further inserts into chromosomes of the host cell. Therefore, the proteins and genetic materials required for virus growth are produced by the host cell. Under the enzyme catalysis, proteins and genetic materials are assembled and released from the cell, thus the host cell is destroyed.
The virus recognizes the receptors on a cell surface, for example, HIV recognizes CD4 and CCR5 antigens on T lymphocyte surface and then enters the cell. However, coronavirus recognizes aminopeptidase-N on lung or kidney cell surfaces, which is the structure of CD13 receptor, for invasion. Therefore, the main direction in developing biotechnology against viruses is to design a drug to interrupt the interaction between virus and surface antigens, so as to prevent virus invasion. However, besides the structure of the above-mentioned for pathogenesis, some virus has another portion just like a super-antigen to interact with host immune system, which directly binds to a T lymphocyte surface receptor, and then induces interleukin or γ-interferon production heavily from T lymphocyte, resulting in drastically inflammatory response and even triggering the linked T lymphocyte to death (such as programmed cell death apoptosis). Therefore, by elimination of the binding elements of a binding event between super-antigen and cell surface antigen, the viral invasion is suppressed, and the infection symptoms is possibly prevented or alleviated.
T lymphocyte cell membrane exhibits its own T lymphocyte receptor (TCR) in the immune system. There are approximately one million mature T lymphocytes patrolling in the human body. Therefore, TCR is used for monitoring the messages from cells or antigen-presenting cell membranes in the body. An antigen-presenting cell exhibits a Major Histocompatibility Complex (MHC), which is capable of recognizing foreign proteins. MHC and a peptide fragment bind together to form a complex, which is then presented on the surface of cell membrane. Thus, the complex formed by MHC and the peptide will specifically release a message to TCR, which acts as a mediator for self and non-self recognition. However, from the scientific research, it has been found that a certain part of the SARS (severe acute respiratory syndrome) virus envelope spike protein binds to a T lymphocyte receptor after invasion. Moreover, the message of mis-recognizing the immune cell results in a release of cytokines immediately without the involvement of MHC molecule through an antigen-presenting cell system. Therefore, T lymphocytes are induced to largely proliferate or produce a vast amount of cytokines, which attack vigorously back to cells and result in inflammatory response. Based on the above study, it is sure that the SARS spike protein exhibits the “super-antigen” property. However, the position of amino acid sequence where the super-antigen fragment is located is still under investigation. Recently, it has been speculated that the super-antigen position is located at the SARS spike protein amino acid sequence 680 to 1050, however, the exactitude needs to be further confirmed.
To prevent the autoimmunological response resulting from SARS virus invasion, a vaccine-like protection system can be utilized. The key point of vaccination is to trigger the originally existing antibody of the infected host with the lymph cell that carries memories of invasion for response. The inventor of the present invention found that the strategy of “induction antibody effectively with a fusion protein” can proceed to a “partial immunization of a super-antigen”. The strategy is designed to provide a fusion protein with partial super-antigen of the SARS virus to a healthy human, and a higher titer of antibody is anticipated, wherein the antibody is induced from the immune cells which are capable of recognizing SARS virus super-antigen regions. During infection, the antibody will capture the super-antigen region of SARS virus and this results in alleviating super-antigen induction or inflammatory response without over-stimulating T lymphocyte proliferation. The inventor of the present invention also utilizes the prior investigation of “fusion protein transporting system”, to find out the “antibody induction of CD13 cell receptor binding region”. Thus, the induced antibody can suppress SARS virus invasion and the SARS infection is prevented.
To begin the experiments for SARS virus investigation, the first concern is to obtain the SARS virus. However, the virus is transmitted by droplet contact, thus the highly infectious virus must be isolated in an appropriately-equipped laboratory. Even though scientists have already sequenced the wild-type SARS virus genome, an ex vivo synthesis of vast amount of viruses is still dependent on a specific host system, which limits the investigation. In the present invention, the inventor translates the amino acid sequence of SARS wild-type virus into specific protein which is published via the Internet. The codons in the amino acid sequence of the SARS virus are modified with translating-effective codons of the ordinary E. Coli host system, and the modified sequence is synthesized by sequential PCR. SARS proteins are further expressed effectively by a conventional E. Coli host system. The present invention aims to acquire a SARS antigen without adopting a virus gene entity, which is beneficial for SARS virus research.